Primary surface heat exchangers have been developed which incorporate thin alloy metal sheets, such as stainless steel that have been corrugated or folded in the nature of pleating. Heat, from a donor fluid, is transferred directly through the sheets to a recipient fluid. The sheets are suitably welded together around their peripheries to prevent the mixture of the donor and the recipient fluids. The corrugations in the sheets serve to support adjacent sheets in a stacked array forming an air cell of a heat exchanger assembly.
Before the sheets are stacked in the air cell, the edge portions of each sheet are crushed or flattened between dies to provide a flat transition or header sections. These transition sections are positioned at each end of the individual sheets and when stacked in the air cell receive the media and deliver the fluid to the appropriate passages formed on both sides of each sheet.
An example of the one such stacked plate heat exchangers of the type described is illustrated in U.S. Pat. No. 4,352,393 to Gonzalo D. Vidal-Meza on Oct. 5, 1982. The transition sections extend generally transversely to the corrugations, and the corrugations are flattened along a central plane. Other examples of flattening along a central plane are disclosed in U.S. Pat. No. 4,346,582 to John M. Bailey on Aug. 31, 1982 and U.S. Pat. No. 4,434,637 to John M. Bailey on Mar. 6, 1984.
When two primary sheets are laid together to form the air cell, the crushed areas form a manifold area. Opposite manifold areas are created within air cells to provide entry and exit of hot exhaust gasses, donor fluid, and cold air, recipient fluid. When heat exchangers or recuperators are used with high pressure ratio gas turbine engine, above about 10 to 1, the density of the air on the cold side, recipient fluid, increases resulting in an increase in the imbalance in fluid densities. While the recuperator is intended to be an energy saving device when used with the gas turbine engine, the donor and recipient fluid flowing through the recuperator losses pressure head. The net effect of this pressure head is a loss in developed power of high pressure gas turbine engines. Therefore, the minimization of the pressure head loss is desirable.
The present invention is directed to overcome one or more of the problems as set forth above.